Home / Math and Physics Files / Physics / Transmission Lines / Notes By Chapter and Appendix / Appendix D EB round
Repair of Appendix D for m = 0 error REVEIWED
DOCX · 77.3 KB
Open DOCX file
Working note by Phil, signed PhL and dated 3.6.14, repairing an error found only in the m = 0 results of Appendix D. He rechecks the coefficient solutions (D.2.28) with Maple, resolves the 0/0 ratio when a0 = 0, and re-derives the E and B field summaries (D.2.33, D.4.8). It ends with a corrected m = 0 field summary (D.6.1) for a round wire, with three mistakes fixed.
AI-written summary; may contain errors. This description is approximate.
Extracted text (machine-read; may contain errors)
Repair of Appendix D for m = 0 error PhL 3.6.14
Just as it says, I found an error ONLY in the Appendix D results for m = 0. I guess this error did not affect the comparison with Chapter 2 or I would have found it earlier. I think is all OK.
I luckily found an error today and will now attempt to fix it.
Here first is a review of the math with Maple verification. I start off with
First summary of the E field solutions (D.2.21)
Ez(r,m) = - j (β'/βd) Jm(x) x = β'r (D.1.27)
Er(r,m) = am x-1 Jm(x) + Jm+1(x) β'2 = β2 - βd2 (D.2.11)
jEφ(r,m) = - am x-1 Jm(x) + ( + ) Jm+1(x) (D.2.15)
and I want to apply these two boundary conditions,
Er(r=a,m) = (jω/σ) Nm (D.2.26)
Eφ(r=a,m) = 0 (D.2.27)
The boundary conditions then say, in terms of the last two equations in (D.2.21),
am xa-1 Jm(xa) + Jm+1(xa) = (jω/σ) Nm (1)
- am xa-1 Jm(xa) + ( + ) Jm+1(xa) = 0 . (2) OK
I now enter these equations into Maple and have it solve for am (= am_s) and Km ( = Km_s),
Then I enter my solutions and see if they are the same,
The only other thing to check is the sum thing:
So I am convinced that my general results are correct as stated in (D.2.28).
am = (jω/2σ) 2m Nm . => a0 = 0 (D.2.28)
= (jω/2σ) Nm [ – ] => = (jω/σ) N0 // J-1(z) = - J1(z)
(+ ) = (jω/2σ) Nm [ + ]
and I rewrite the first one as
= (jω/2σ) 2 Nm . (5)
The issue at hand is the above ratio when m = 0. We know that a0 = 0 from (D.2.28) and of course m = 0 so we have a 0/0 situation. The correct ratio is given by (5) above,
= (jω/2σ) 2 N0 = - (jω/2σ) 2 N0
but I accidentally set this ratio to to zero in several places! So I keep marching through Appendix D now.
I verified (visual tracking) all the algebra of inserting the coefficients(D.2.28) into (D.2.21) to get (D.2.33). That algebra luckily is written out above (D.2.33).
Second summary of the E field solutions : Rdc = β'2 = β2 - βd2 (D.2.33)
Ez(r,m) = (1/4) ηm I Rdc (aβ') [ - ] a = radius ηm ≡
Er(r,m) = (j/4) ηm I Rdc (aβd) [ + - ] x = β'r
Eφ(r,m) = (1/4) ηm I Rdc (aβd) [ - + + ] xa = β'a
My next collection however goes back to the coefficients, it is (D.4.9), and this is the box that I used to do the m = 0 reductions:
Ez(r,m) = - j (β'/βd) Jm(x) x = β'r β'2 = β2 - βd2
Er(r,m) = am x-1 Jm(x) + Jm+1(x) .
jEφ(r,m) = - am x-1 Jm(x) + ( + ) Jm+1(x) (D.2.21)
Bz(r,m) = (β'/ω) ( + )Jm(x)
Br(r,m) = j(β'/ω){ + ( m - am) x-1Jm(x) + ( + ) Jm+1(x) }
Bφ(r,m) = (β'/ω){ - ( m - am) x-1Jm(x) + ( + ) Jm+1(x) } , (D.4.8)
The key facts are:
(+ )|m=0 = (jω/2σ) N0 [ + ] = (jω/2σ) N0 [ - ] = 0
= (jω/σ) N0 =
Here then is my corrected (D.6.1)
Summary of E and B fields inside a round wire ( m = 0 only ) (D.6.1)
Ez(r,0) = - j (β'/βd) J0(x) // large a0 = 0 x = β'r β'2 = β2 - βd2
Er(r,0) = J1(x) . // small = (j/2) (aβd) I Rdc
jEφ(r,0) = 0 // small Rdc =
Bz(r,0) = 0 // small ~ β'
Br(r,0) = 0 // very small ~ βd
Bφ(r,0) = (β'/ω) ( + ) J1(x) // large ~ β' (β'/βd)
Ouch, I have not one but three mistakes in this box.
I did a long round of edits just now in lines doc, see edit log, and I included the above fixes.